This invention relates to a method for isolating imperfections in semi-insulating GaAs wafers used in the fabrication of metal-semiconductor field effect transistors (MESFETs) and integrated circuits.
Semi-insulating GaAs material grown by Liquid Encapsulation Czochralski (LEC) techniques is currently used as starting material for direct ion implanted MESFET and integrated circuit fabrication. The semi-insulating characteristic (resistivity typically in the range of 10.sup.7 ohm-cm to 10.sup.10 ohm-cm) of the GaAs material is formed during LEC growth. GaAs wafers made from this starting material display poor intrinsic material properties, such as purity, uniformity, and electron mobility. These properties are inherent in the material as a result of LEC crystal growth and have a significant impact on the speed performance and yield of fabricated devices. However, significant improvement of these properties during LEC growth is difficult because of insufficient growth control capability. Therefore, improvements after LEC growth are a more practical approach. One way to accomplish this is by extrinsic gettering techniques. The aim of extrinsic gettering is to isolate imperfections, such as impurities, structural defects, and precipitates, by moving the imperfections away from the active area in the semi-insulating GaAs material to other areas (the wafer backface, for example) where they have minimum effect on device performance.